This strategy consists of synchronizing the sea surface temperature SST al recorded in marine cores with the air temperature al recorded in polar ice cores. Similarly, the dating uncertainty of the alignment tie points defined with respect to AICC is the dating error given in ref. The modern surface water reservoir age at a given site is then obtained from the nearest grid node to the core site Fig. This spatially varying component of the reservoir age is subtracted from the laboratory 14 C age before calibration with error propagation.
In those cores, we used alignment tie points to complement calibrated 14 C dates when the latter were too sparse. The salinity section illustrates the distribution of the cores with respect to the main modern water masses.
Moreover, this age-depth modeling routine computes a conservative age-depth uncertainty, through the provision of bootstrapping and sediment accumulation rate uncertainty 49 Fig. In the presence of age reversals, we progressively increased the bootstrapping percentage in order to make sure that the dating uncertainty computed by Undatable was large enough to encompass most calibrated 14 C ages, leaving out only outliers beyond 2 sigma dating uncertainty.
NGRIP alignment targets correspond to the rapid transitions out of and into Greenland stadials, as dated and listed in refs 2931 Online-only Table 2.
studies have demonstrated that changes in air and sea surface temperature were synchronous across the last deglaciation 9 and some of the last glacial rapid climate changes 10 over the North Atlantic region. Blue, yellow and red probability density functions indicate the radiocarbon and alignment tie points, and tephra age-depth constraints, respectively.
Consistently dated atlantic sediment cores over the last 40 thousand years
In rare cases, rapid and well-defined coolings have been aligned. Similarly, one single person defined all the alignment tie points in the three Brazilian cores. Try out PMC Labs and tell us what you think. MS tie points and their associated uncertainties were defined using the same method as described for the alignment of SST als to ice core records. In contrast, this dating approach gives access to the relative timing of circulation changes recorded at different water depths in cores located on depth transects.
The same is true at all latitudes during the Holocene. To date, these rapid changes in climate and ocean circulation are still not fully explained. The dating procedures 1 - 3 are described in detail below. This new data set enables paleoclimate scientists to i examine relative phases between Atlantic records e.
Thus, in mid and low latitudes, and during the Holocene at higher latitudes, the sediment cores were dated by means of calibrated radiocarbon ages. For consistency, the alignment tie points in high latitude cores were all defined by the same person. Machine-accessible metadata file describing the reported data ISA-Tab format.
Here we focus on the last 40 ky because it is the time span covered by radiocarbon dating and the sole period for which it is possible to establish calendar age timescales dating marine cores with a precision approaching that of ice core or speleothem records. The MS records of four of these five cores have been ly shown to be in phase with the Greenland air temperature al This can be explained by the fact that changes in MS arise from changes in the efficiency of the transport of fine grained magnetic particles by deep currents from the source to the site of deposition The fact that the MS al is in phase in cores located north and south of the sills separating the Nordic Seas from the North Atlantic age, suggests that the source of magnetic minerals could be at the sills, with the strength of the overflow from the Nordic Seas directly proportional to the strength of the inflow into the Nordic Seas.
In mid and low latitudes i. Not fulfilling this condition would result in negative surface reservoir ages, which is not physically possible see Supplementary Fig. SST alignment to Antarctic temperature variations was made at marked transitions in the temperature record, such as Antarctic Isotopic Maxima 32 Atlantic, the onset of the early and late deglacial warming, or the beginning of the Antarctic Cold Reversal.
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For pre-Holocene dates, a minimum of 14 C yr is used instead of 14 C yr. Example of age-depth plot produced by Undatable. In a few cases, when the SST record resolution was too low or the al shape ambiguous, maxima or minima have been aligned. Both age and depth uncertainties are defined for each tie point.
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Moreover, this data set is of direct use in paleoclimate modeling studies. In instances of ambiguities that could not be age by the constraints provided by 14 C dates, we attributed an uncertainty to the depth of the tie point, large enough to encompass the two events warmings, or more rarely, coolings or SST maxima or minima which could both be aligned to the same target.
In all other cases, dating uncertainties are larger. One obstacle hindering progress in our understanding of the interactions between past ocean circulation and climate changes is the difficulty of accurately dating marine cores. In order to decipher the mechanisms at play in observed Atlantic climate changes, it is necessary to establish a common temporal framework for paleoclimate records from different archives and from different locations.
Location of the 92 dated Atlantic sediment cores see Online-only Table 1 for precise coordinates and water depths of the cores. Dating, modeling studies of the last deglaciation 11 or last glacial millennial climate changes 1213 show that both increases and decreases in North Atlantic Southern Ocean SST and in air temperature above Greenland Antarctica dating synchronous. The grey cloud indicates the probability density cloud of the age-depth model, whereby darker colors indicate higher age-depth probability. Moreover, a common chronology for Greenland and Antarctica ice cores has been developed based on their records of 10 Be and atmospheric CH 4 concentration 15 Using the GICC05 and AICC age scales as alignment targets for high latitude SST records of the north and south hemispheres respectively, it is thus possible to directly compare marine records from both hemispheres on a common time frame.
To for this temporal change in surface reservoir age, we linearly scaled a reservoir age correction to atmospheric pCO 2whereby a correction of 0 14 C y corresponds to present day pCO 2and 14 C y to LGM pCO 2. Thus, in the best cases, when bioturbation biases and local changes in past surface reservoir ages remain limited, sediment core dating uncertainties mainly arise from the conversion of radiocarbon ages into calendar ages.
This new rapid age-depth modeling routine was ideal for this project as it allowed us to run and re-run age models for the many sediment cores that we have analyzed. When SST reconstructions based on full Atlantic count data were not available, we used the percentage age the polar species Neogloboquadrina pachyderma left coiling as a proxy for SST. This approach has been described and validated in a of studies e. studies have revealed that surface reservoir ages have not remained constant over time at high latitudes of the North Atlantic and Southern Ocean i.
The blue and black broken lines represent The red line indicates the age-depth model median. Learn More. These values can be downloaded from Figshare To also consider temporal changes in reservoir age, we further applied a correction to for the impact of atmospheric CO 2 concentration changes upon surface water 14 C activity. Here we adopt a strategy that has been widely applied e. Also, we considered tephra layers as the most reliable age-depth constraints and, therefore, a priori excluded them from the bootstrapping process e.
We ed for both spatial and temporal variability in 14 C reservoir ages. This way, we take into increased dating uncertainty associated with the existence of age-depth scatter, which may be related to sedimentation hiatuses, abundance changes, or bioturbation.
Here, we present a set of 92 marine sediment cores from the Atlantic Ocean for which we have established age-depth models that are consistent with the Greenland GICC05 ice core chronology, and computed the associated dating uncertainties, using a new deposition modeling technique. Also, the SST records used in the present study are all based on planktonic foraminifer census count data.
In those high-latitude regions, it is thus necessary to use an alternative dating strategy in lieu of 14 C dating of marine organisms. Almost all our age-depth models of low- and mid-latitude cores 51 out of the 92 cores, see Online-only Table 1 are entirely based on calibrated 14 C ages.
Even in regions where surface reservoir ages can be predicted based on the evolution dating atmospheric CO 2as described above, increased uncertainties in radiocarbon-dated chronologies can still arise from bioturbation biases e. The depth uncertainty directly depends on the sampling resolution of the SST curve: Atlantic is taken as half of the depth interval corresponding to the rapid warming or more rarely coolingor as half of the width of the SST maximum or minimum, when maxima or minima have been aligned.
Tie points were generally defined by aligning rapid warmings recognized in both the ice core and marine core, as recommended in ref. This age-dependent component of the reservoir age is added to the IntCal13 or SHCal13 14 C age record before calibration. Remaining age in the identification of alignment tie points were solved in most cases by fulfilling the condition that the tie point age is younger or equal to the calibrated 14 C ages obtained by assuming no other change in surface reservoir age than the temporal evolution due to changing atmospheric pCO 2.
Radiometric dating and paleontologic zonation
In three cores GeoB, MD and MDQlocated on the Brazilian age in a region under the influence of the Intertropical Convergence Zone, it is possible to take advantage of the simultaneous recording of rainfall increases during Greenland stadial periods in the marine cores and in U-Th dated speleothems from the adjacent continent to dating the marine age models.
In some North Atlantic cores 7 out of 92, cf. Support for this synchronicity comes from tephra and geomagnetic field Laschamp inclination excursion marine records. Importantly, the speleothem record from El Condor cave 26to which we have aligned the three marine cores, has been shown to be in phase, within dating uncertainties, with the NGRIP air temperature record in Atlantic GICC05 age scale 25 We used different types of chronological markers to derive these 29 age-depth models:. The alignment procedures 1 and 2 by essence impede the assessment of le and lags between the aligned records.
The error used for this spatial reservoir age component is either the computed GLODAP standard deviation, or 14 C yr, whichever is greater. New cores were added to fill gaps with respect to the available geographical and water depth coverage, and additional radiocarbon dates were produced to improve the existing age models of some cores Online-only Table 1.
A first alignment target is based on the observation that the cooling marking the beginning of Heinrich Stadial 1 in three independently dated North Atlantic cores is synchronous with the sharp increase in dust flux recorded in the Greenland ice cores and dated at This observation is consistent with this cooling being coeval with an Atlantic in dust transport from Asia to Greenland, as observed during other Greenland stadials Two other alignment targets correspond to the beginning and the end of dating warm event identified in ref.
These marine records become aligned with tephra and cosmogenic nuclide Greenland records when the MS tuning to Greenland is applied e. Rapid changes in ocean circulation and climate have been observed in marine-sediment and ice cores over the last glacial period and deglaciation, highlighting the non-linear character of the climate system and underlining the possibility of rapid climate shifts in response to anthropogenic greenhouse gas forcing. Age, paleoclimate data-model integration studies, such as groundtruthing of transient modeling analyses, timeslice comparisons of proxy data, or data assimilation, necessitate consistent paleoclimate records chronologies in calendar years.